Vehicles comprising spring-mounted vehicle seats are known in particular for damping a height excursion of the vehicle seat when travelling over uneven road surfaces, such as potholes. EP 1 188 608 A1 discloses a damping system for spring-mounted vehicle seats, in which a pneumatic load relief device and a hydraulic actuator are arranged between a seat part and a lower part connected to the vehicle, in addition to a mechanical flexible connection device. Both the pneumatic load relief device and the hydraulic actuator are controlled by a control device as a function of a seat error signal, which is generated for example by a sudden height adjustment of the seat part.
Such suspension devices are of simple construction since the actuator, upon receipt of a position error signal relating to the vehicle seat, which is acted upon by the weight of the driver, is supplied with air by means of a compressor and as a result an increased volume of air is provided for sufficiently damping the vehicle seat. Such suspension devices do not have along their height adjustment any comfort range which extends over a relatively long portion of the height adjustment distance, and thus provides a uniform suspension within this height adjustment range with the same restoring forces.
Also known are air springs which have a linearly running force/distance air spring characteristic, the gradient of which differs depending on the design of the air spring and an applied additional volume. Usually with such air springs, constant additional volumes are used which are connected to the expanding and contracting air spring as an actual air volume of the air spring. Such constant additional volumes have the result that, when the air spring is set with a force/distance air spring characteristic having a small gradient, it is not possible for the seat part to return to a central position of the force/distance air spring characteristic since friction forces within the suspension device as a whole are greater than a restoring force within the force/distance air spring characteristic. On the other hand, when the suspension device is designed in such a way that the restoring force is greater—i.e. a greater gradient of the air spring characteristic is set—relatively hard damping is achieved both in the middle stroke range and in the end stroke ranges of the air spring. Furthermore, when using an air spring with a small gradient, there is a high risk that the end stops in the stroke end regions of the air spring will be reached in the event of pronounced expanding and contracting movements caused by a considerable unevenness, which results in a reduced seating comfort for the user of the vehicle seat.
The abovementioned suspension systems have in common the fact that they are usually used for vehicle seats as suspension systems which can be actively influenced. The function of these suspension systems is usually considered independently of the function of any additionally present suspension of the vehicle cab. Therefore, only a vibration acting on the vehicle seat, caused either by the spring-mounted vehicle cab or by the vehicle frame, is taken into consideration in order to bring about a reaction in the suspension system of the vehicle seat for the optimal suspension of the vehicle seat. On the other hand, however, an active control of the suspension movement of the utility vehicle cab as a function of the actively influenced suspension movement of the vehicle seat taking account of the excursion of the vehicle frame does not take place. Instead, one combination which is often used is a passively controlled suspension movement of the vehicle cab, which does not provide for the switching on and off of additional volumes but rather uses for example only an intrinsically closed air spring, with an actively controlled suspension movement of the vehicle seat, which may take place for example by means of an additional volume. This disadvantageously results in the high probability that either the spring element of the vehicle cab or the spring element of the vehicle seat or both reach their end stop regions when a considerable excursion of the vehicle frame takes place when travelling over a pothole. It is also found inter alia that, for subsequent spring movements, in some circumstances the full spring travel of the spring elements of the vehicle seat and/or of the vehicle cab and/or possibly of damping elements provided instead or in addition is no longer available.